Various types of differential assemblies are used in motor vehicles to redirect the transfer of power to the driving axles. In a rear-wheel drive vehicle, the transmission shaft from the gearbox turns the differential through a crown wheel and pinion. In a front-wheel drive car, the gearbox may drive the differential directly through a pair of helical spur gears. Four-wheel drive vehicles have two or three differentials, one for each driving pair of wheels and sometimes one between the front differential and the rear differential. All differentials allow the axle stub shafts or drive shafts, and subsequently, the wheels of the vehicle to be rotated at varying speeds as needed. In general, the side gears (which are connected to the axle stub shafts) and the pinion gears mesh to redirect the transfer of power to the driving axles/shafts.
In a typical differential gear arrangement, the drive pinion gear turns the differential input gear and the differential case attached to it. The differential pinion gears that are mounted in the case mesh with the differential side gears that are splined to the differential output shafts. In front-wheel drive vehicles, the drivetrain is often compacted into an engine/transaxle/driving axles "package" that provides torque to the front wheels. The transaxle assembly, comprising the transmission and the differential assembly, is often shipped modularly from vehicle powertrain plants to vehicle assembly plants to be installed in the vehicle. At the assembly plant, the axles are installed to the differential assembly by meshing them with the side gears. Once the axles have been installed, the transmission and differential assembly become enclosed and appropriate lubricating fluids are added to various components.
A disadvantage of conventional differential assemblies in front wheel drive transaxles is that they cannot be filled with lubricant until the drive shafts are installed at the assembly plant. Because the side gear and axle shafts are not assembled until they reach the assembly plant, the transaxle is not enclosed and is vulnerable to the ambient environment; therefore, special shipping and handling procedures are required to assure undamaged components. Moreover, valuable time and manpower are used at the final assembly plant for filling specific components with appropriate fluids following the installation of the axles into the differential assembly.
Additionally, the transaxle cannot be washed after filling since it is already assembled in the vehicle. Any spillage may be perceived as leakage by the customer. This causes unnecessary dissatisfaction and warranty cost. Also, filling in the vehicle is less accurate due to temperature variance and level inaccuracies.